We are studying changes with aging in A/Jax female mice of several immunologic responses, especially of tuberculin-type delayed hypersensitivities to the antigens conalbumin and methylted human serum albumin. This long-term study will continue. In addition, we shall begin to investigate cellular and molecular reasons for increased reactivity that the aging mice have already shown early in their aging (at 6 months) and greatly decreased reactivity that they have shown at 18 months of age. We are also studying the apparent connection between accelerated aging in SJL/J mice and their monocyte/macrophage hyper-reactivity which, in turn, seems due to the propensity of this strain of mice to react, more than other strains, to antigens in their food. Experiments in both of these strains of mice include, especially, characterization of peritoneal and blood monocytes, and analyses of changes in seven serum antigens that we have detected in aging mice by crossed immunoelectrophoresis.